Moiré superlattices, a twisted functional structure crossing the periodic and nonperiodic potentials, have recently attracted great interest in multidisciplinary fields, including optics and ultracold atoms, because of their unique band structures, physical properties, and potential implications. Driven by recent experiments on quantum phenomena of bosonic gases, the atomic Bose–Einstein condensates in moiré optical lattices, by which other quantum gases such as ultracold fermionic atoms are trapped, could be readily achieved in ultracold atom laboratories, whereas the associated nonlinear localization mechanism remains unexploited. Here, we report the nonlinear localization theory of ultracold atomic Fermi gases in two-dimensional moiré optical lattices. The linear Bloch-wave spectrum of such a twisted structure exhibits rich nontrivial flat bands, which are separated by different finite bandgaps wherein the existence, properties, and dynamics of localized superfluid Fermi gas structures of two types, gap solitons and gap vortices (topological modes) with vortex charge S = 1, are studied numerically. Our results demonstrate the wide stability regions and robustness of these localized structures, opening up a new avenue for studying soliton physics and moiré physics in ultracold atoms beyond bosonic gases.

A passively switchable erbium-doped fiber laser based on alcohol as the saturable absorber (SA) has been demonstrated. The SA is prepared by filling the gap between two optical patch cords with alcohol to form a sandwich structure. The modulation depth of the alcohol–SA is measured to be 6.4%. By appropriately adjusting the pump power and the polarization state in the cavity, three kinds of mode-locked pulse patterns can be achieved and switched, including bright pulse, bright/dark soliton pair, and dark pulse. These different soliton emissions all operate at the fundamental frequency state, with a repetition rate of 20.05 MHz and a central wavelength of ∼1563 nm. To the best of our knowledge, this is the first demonstration of a switchable soliton fiber laser using alcohol as the SA. The experimental results further indicate that organic liquid-like alcohol has great potential for constructing ultrafast lasers.

We demonstrate the generation of a unique regime of multiple solitons in a Tm-doped ultrafast fiber laser at ∼1938.72 nm. The temporal pulse-to-pulse separation among the multiple solitons, 10 in a single-pulse bunch, increases from 0.89 ns to 1.85 ns per round trip. In addition, with the increasing pump power, the number of bunched solitons increases from 3 up to 24 linearly, while the average time separation in the soliton bunch varies irregularly between ∼0.80 and ∼1.52 ns. These results contribute to a more profound comprehension of nonlinear pulse dynamics in ultrafast fiber lasers.

The present study is devoted to investigate the chirped gap solitons with Kudryashov’s law of self-phase modulation having dispersive reflectivity. Thus, the mathematical model consists of coupled nonlinear Schrödinger equation (NLSE) that describes pulse propagation in a medium of fiber Bragg gratings (BGs). To reach an integrable form for this intricate model, the phase-matching condition is applied to derive equivalent equations that are handled analytically. By means of auxiliary equation method which possesses Jacobi elliptic function (JEF) solutions, various forms of soliton solutions are extracted when the modulus of JEF approaches 1. The generated chirped gap solitons have different types of structures such as bright, dark, singular, W-shaped, kink, anti-kink and Kink-dark solitons. Further to this, two soliton waves namely chirped bright quasi-soliton and chirped dark quasi-soliton are also created. The dynamic behaviors of chirped gap solitons are illustrated in addition to their corresponding chirp. It is noticed that self-phase modulation and dispersive reflectivity have remarkable influences on the pulse propagation. These detailed results may enhance the engineering applications related to the field of fiber BGs.

The parameter dynamics of super-sech and super-Gaussian pulses for the perturbed nonlinear Schrödinger’s equation with power-law nonlinearity is obtained in this article. The variational principle successfully recovers this dynamical system. The details of the variational principle with the implementation of the Euler–Lagrange’s equation to the nonlinear Schrödinger’s equation with power-law of nonlinearity described in this paper have not been previously reported.

Breathing solitons, i.e., dynamic dissipative solitons with oscillating pulse shape and energy caused by different mechanisms of spatiotemporal instabilities, have received considerable interest from the aspects of nonlinear science and potential applications. However, by far, the study of breathing solitons is still limited within the time scale of hundreds of cavity round trips, which ignores the slow dynamics. To fill this lacuna, we theoretically investigate a new type of vector dissipative soliton breathing regime and experimentally demonstrate this concept using mode-locked fiber lasers, which arise from the desynchronization of orthogonal states of polarization (SOPs) in the form of complex oscillations of the phase difference between the states. The dynamic evolution of polarization states of the vector breathings solitons takes the form of a trajectory connecting two quasi-equilibrium orthogonal SOPs on the surface of the Poincaré sphere. The dwelling time near each state is on the scale of a tenth of a thousand cavity round trip times that equals the breathing period, which is up to 2 orders of magnitude longer than that for common breathers. The obtained results can reveal concepts in nonlinear science and may unlock approaches to the flexible manipulation of laser waveforms toward various applications in spectroscopy and metrology.

The objective of the present study is to examine the behaviors of chirped optical solitons in fiber Bragg gratings (BGs) with dispersive reflectivity. The form of nonlinear refractive index represents polynomial law nonlinearity. By virtue of phase-matching condition, the discussed model of coupled nonlinear Schrödinger equation is reduced to an integrable form. Consequently, chirped optical solitons having various profiles such as W-shaped, bright, dark, kink and anti-kink solitons are derived. Further to this, the chirp associated with these soliton structures are extracted. The impact of dispersive reflectivity, self-phase modulation and cross-phase modulation on the pulse propagation is investigated and it is induced that the changes of self-phase modulation and cross-phase modulation cause a marked rise in soliton amplitude which is subject to minor variations by dispersive reflectivity. The physical evolutions of chirped optical solitons are described along with the corresponding chirp to pave the way for possible applications in the field of fiber BGs.